Transfer mechanism of defects on topcoat to resist pattern in immersion lithography process and effects on etching process

摘要

For the scaling down of the semiconductor design rule, 193-nm lithography technology is entering the 65-nm-node generation. In 65-nm and finer processes, the practical application of 193-nm immersion lithography is progressing due to its high numerical aperture (NA), which is achieved by using de-ionized water (DIW) as the medium between the lens and wafer in the exposure system. Immersion lithography, however, generates two main concerns: the penetration of moisture into resist film and the leaching of resist components into DIW as a result of immersing the resist film in DIW. To prevent these effects, the use of a topcoat process has been adopted, but there have been reports that defects caused by remaining droplets on the topcoat or particles can be transferred to the resist pattern and degrade resolution. Research to date has clarified the generation mechanism of defects due to water droplets, and the importance of preventing droplets from remaining is now understood. However, there are few research reports on the generation of particles, and to reduce defects caused by the immersion process. It is essential that the generation mechanism of particle-related defects on the resist pattern be clarified and that a suitable approach to reducing particles is needed. It is also known that particles on the resist pattern that acts as a mask in the dry etching process can be associated with defects in etching, which makes particle control in the process steps between lithography and dry etching all the more important. In this paper, we clarify the defect-generation mechanism on resist pattern due to particles put on topcoat and investigate the effects of such particles on the dry etching process.